In the art, waterbeds are comprised of water-filled bladder-type mattresses supported at their bottoms and about their sides by horizontal decks and vertical side and end walls of related bed frame structures. It has long been common practice to heat the water within the mattresses to temperatures which are most comfortable for the users of the beds. The water in waterbed mattresses is commonly heated by electric resistance heater units positioned between the bottoms of the mattresses and the decks of their related frame structures. The heater units are supplied with electric current through electric service cords which extend from the heaters and the bed structures to common electric power service outlets in the rooms or buildings in which the beds are used.
In the case of most waterbed heater units, manually adjustable temperature control devices are engaged in the service cords. The control units include thermostatic switches controlling the flow of current in the heater units and include temperature sensing devices, such as thermocouples, which are arranged to contact the mattresses at locations remote from the heater units so that the thermostatic switches operate in response to the mean temperature of the water in the mattresses, not the temperature of the water imediately adjacent or close to the heater units.
Ordinary waterbed mattresses are from 84 inches long, 48 inches to 72 inches wide, and from 7 inches to 8 inches in depth or vertical extent. Accordingly, the volume of water in such mattresses is substantial and establish excellent heat sinks which absorb heat generated by related heater units and which disperses that heat throughout the mattresses at a rate which is sufficiently close to the rate at which heat is generated by the heater units. The rate at which the heat is dispersed throughout such mattresses is such that an accumulation of heat and overheating of the bed structures adjacent the heater units will not occur during normal and intended use of the waterbed structures. More particularly, the normal volume of water in waterbed mattresses absorbs and disperses the heat generated by related heater units at a rate which is sufficient to keep the temperature of the commonly used polyvinylchloride sheet stock of the mattresses which is in contact with the heater units cool and well below those temperatures at which the plastic material commences to degradate and/or burn.
While the foregoing results in or provides suitably heated waterbed structures that are safe to operate and use under ordinary and intended operating conditions, the heater units, with and without related temperature control means, are capable of and/or subject to rapidly overheating causing other irreparable damage and injury if and when the volume of water in the mattresses is reduced to an extent that it affords a heat sink which is insufficient and/or inadequate to absorb and disperse heat generated by the heater units at a sufficient rate to prevent accumulation of heat at and about the heater unit; and when the volume of water is reduced to an extent that the weight of persons or other objects positioned atop and supported by the mattresses displace the water above the heater units and allows the tops of the mattresses to "bottom out" or establish bearing contact on the bottoms of the mattresses. When the foregoing occurs, the capacity of the water remaining in the mattresses to maintain the temperature of the sheet plastic of the mattresses and the heater units at safe, non-excessive temperatures is lost. It is also to be noted that due to the necessary displacement or remote positioning of the heat sensing devices of the temperature control units for the heater units, those temperature control units are of little use or value to prevent the adverse effects and damage which is likely to be caused by the heater units when the normal volume of water in the mattresses is reduced or diminished to an extent that adverse effects are likely to result.
As a result of the foregoing laws have been instituted which require the manufacturers of waterbeds and waterbed heaters to boldly display special warnings and instructions to the purchasers and users of waterbeds directing them not to plug in and or connect waterbed heater units with power supplies until the mattresses are filled with water and to unplug or disconnect the heater units from their power supplies before draining of water therefrom is commenced.
While the above warnings and instructions might be expected to be adequate to prevent heat damage of the nature and character noted above, when some purchasers and users of waterbeds and waterbed heaters fill and drain their waterbeds, history and experience indicates that those warnings and instructions are often not understood or are ignored and/or injuries result.
Further and more important, the warnings and instructions noted above are only effective when waterbeds are being filled, emptied or otherwise visually monitored and worked upon. Such warnings and instructions are of no use or value when waterbed mattresses rupture or spring leaks when unattended or when they are in use or occupied by persons who are asleep or incapable of suitably responding to dangerous conditions due to some physical incapacity.
Experience and history indicate that the number of incidents in which overheating of waterbed heater units cause adverse effects and damage to waterbed structures in the course of filling and emptying the mattresses, is in fact negligible compared to the number of incidents in which damage to property and personal injuries occurs as a result of overheating of heater units and their related bed structures caused by the loss or leakage of water from mattresses, when waterbeds are unattended and when they are in use (when written warnings and instructions serve no useful purpose).
To the best of our knowledge and belief, the prior art has long recognized the extreme hazards associated with the loss of water in waterbed mattresses with which heater units are related, but has failed to provided any reasonably effective and commercially practical means to eliminate those hazards.
It is our understanding that the prior has provided at least one independent alarm system to warm of the leakage of water from within the mattresses of waterbed structures and to thereby reduce the hazards caused by such leakage. That alarm system included a water actuated triggering switch arranged in a related waterbed structure beneath the mattress thereof. The switch was closed by water leaked from the mattress and which flowed or migrated into contact therewith. The principal shortcoming of the above noted alarm system resided in the fact that it was subject to being actuated by any liquid (other than water from within the mattress) which might be spilled, condensed or otherwise collect and find its way into the waterbed structure where the switch occured and proved to be highly susceptible to giving false alarms. Further, that alarm system, being an independent or separate system, was sold separately, required independent handling and installation and was considered by the majority of installers and users of waterbeds to be inconvenient and bothersome.